Investigation On Magnetism And Electrical Properties Of Manganite-Based Heterojunctions

Among the manganite oxides, Sr-doped LaMnO₃ have been a focus of intensive studies since the discovery of relatively higher Curie temperature and CMR. Simultaneously, it is noted that Sr-doped LaMnO₃ belong to p type semiconductors and if they are introduced to form heterojunctions, it will be very significant to explore basic science and develop novel devices.LSMO heterostructures were deposited by RF magnetron sputtering in this thesis, and the main contents of the thesis are as follows:1. La_1-xSr_xMnO₃(x=0.3, 0.2, 0.04)/Nb-0.8wt%-SrTiO₃ heterojunction has been prepared, By simulating the parameter,ideal factor n is between 2 and 3, saturation current is around 10-6A, the series resistance is below 10Ω. It can be indicated that all the junctions show excellent rectifying characteristic. With increasing x,series resistance has been lessened and rectifying characteristic has been enhanced.2. Rectifying characteristic of La₀.7)Sr_0.3MnO₃/STON schottky diode from 60 K to 300 K has been investigated. The ideal factor n increases from 2 to 17 with deceasing temperatures because of the excessive tunneling leakage current at low temperatures; series resistance slightly reduced from 2.6Ωto 2.5Ω.That can be attributed to the change of both resistance of LSMO and STON; lnJs linearly varies with T-1, which means that the electrical transport properties of the mentioned heterostructures are mainly affected by the thermal effect.3. La₀.7)Sr_0.3MnO₃(LSMO)/ZnO heterostructures were synthesized by the rf magnetron sputtering and exhibit obviously rectifying properties. The rectify properties can be controlled by O2/Ar ratio for the preparation of ZnO film. The diffusion potentials increase with increasing O2/Ar ratio and decrease with the increase of temperature. Electrical transport property of the mentioned heterostructure is mainly affected by the thermal effect when the temperature is above 220K. At low temperature the I-V curves are impacted by the modulation of the spin-splitting gap of eg electrons in LSMO layer.